Self-expanding prostheses, such as stents, covered stents, vascular grafts, flow diverters, and the like have been developed to treat ducts within the animal body. Many of the prostheses have been developed to treat blockages within the vasculature and aneurysms that occur in the brain. Delivery of a self-expanding prosthesis to a treatment site has traditionally involved securing the prosthesis to an outer distal segment of an elongate polymeric delivery catheter by use of a removable sheath and then advancing the delivery catheter through the vasculature to the treatment site. When properly positioned, removal of the sheath permits the prosthesis to self-expand into contact with the vessel wall being treated. Low-profile wire-based delivery systems were later developed to treat small diameter vessels not accessible by the traditional catheter delivery systems. Wire-based delivery systems generally include an elongate wire, such as a guidewire or hypotube, which has a distal segment configured to carry the prosthesis. A sheath, which may include a delivery catheter, is typically used to restrain the prosthesis on the wire and to assist in the delivery of the prosthesis to the treatment site. U.S. Pat. No. 6,989,024 entitled “Guidewire Loaded Stent for Delivery through a Catheter” discloses such a system.
The ability to accurately place the prosthesis at a treatment site is of paramount importance. Misplacement of the prosthesis will typically adversely impact the efficacy of the intended treatment and, in many instances, will require further patient treatment interventions. For this reason an ability to partially deploy the prosthesis to determine proper placement combined with an ability to return the prosthesis to its original unexpanded configuration, if the placement of the prosthesis is found to be incorrect, is highly desirable. Upon returning the prosthesis to its unexpanded state, the delivery system can be manipulated to place the prosthesis at the proper deployment location. A problem associated with returning the prosthesis to its unexpanded state is that the prosthesis tends to shift proximally on the delivery wire as a result of frictional forces acting on the prosthesis when it is withdrawn into the sheath.
U.S. Pat. No. 7,201,769 entitled “Expandable Stent and Delivery System” discloses a stent and delivery system that includes proximal, intermediate and distal cylindrical members disposed on and spaced apart along an elongated core member such that first and second gaps are formed. The expandable stent includes proximal and distal anchor members which align with the gaps. The expandable stent is mounted on the intermediate cylindrical member, and the anchor members, having a length slightly less than the length of the gaps, are disposed within the gaps thereby locking the stent onto the core member. Interlocking the proximal anchor members within the first gap locks the stent's position during resheathing. One problem with this delivery system is that it requires that gaps be formed on the wire between at least two cylindrical members for interlocking the anchor members. The delivery system also requires the use of an intermediate cylindrical member for mounting the stent. The need to orient at least two cylindrical members together to form each gap on the delivery wire creates design restrictions that can adversely impact delivery system characteristics, such as, for example, flexibility. Moreover, the required use of an intermediate cylindrical member for mounting the stent and for forming the gaps necessarily adds to the radial dimension of the delivery wire and affects its smallest achievable profile. The intermediate cylindrical member also impacts the flexibility of the distal segment of the delivery system by imposing additional stiffness.